Thursday January 17 2008
Black women develop breast cancer 21 years younger than white women
Black women are more likely to develop breast cancer younger than white women, reports The Times and other newspapers. New research has shown “that black patients had breast cancer diagnosed on average at 46 while white patients had a diagnosis at an average age of 67”, the newspaper said. In addition, “the survival rate was poorer among black women and their tumours are likely to be aggressive”, according to The Daily Telegraph.
The newspaper reports are based on a study in Hackney, east London, that investigated the rates of breast cancer in black women. The results have led to suggestions that there may be biological differences in the development of the disease. More research covering a wider range of socioeconomic factors, screening uptake rates, attitudes to treatment and access to care is needed, as well as the biological explanations offered by the researchers.
Where did the story come from?
The research was conducted by Dr Rebecca Bowen from the Centre for Tumour Biology, Institute of Cancer in London and other colleagues from the UK. The study was supported by the Gordon Hamilton Fairley Fellowship, Cancer Research UK, and Barts and The London Charitable Foundation. It was published in the peer-reviewed: British Journal of Cancer.
What kind of scientific study was this?
This was a cross-sectional study conducted by a retrospective review of clinical notes. The researchers looked at the notes of all women with invasive breast cancer attending an east London hospital between 1994 and 2005. They compared the age distribution and the clinical and microscopic features of the tumours found between black women and white women. They also took into account what effects socioeconomic status might have on the differences between the ethnic groups.
The researchers excluded the notes of patients where ethnicity had not been recorded and those from other ethnic groups (for example Indian, Greek or Jewish). There were 445 patients with a new diagnosis of breast cancer during this period, and 152 were excluded form the analysis. This left available data on 102 black women and 191 white women
What were the results of the study?
The age at diagnosis of breast cancer was 67 for white women and 46 for black women. The study was carried out in Hackney. In order to check that this difference in age at diagnosis was not related to a difference in the age ranges of black and white people in the borough, the researchers used census data to confirm that the populations were similar.
Black women also had a higher rate of the more severe (grade 3) tumours. In addition, they also had more lymph nodes affected by the disease and a higher incidence of basal-like tumours which are more difficult to treat.
The researchers said that there were no differences in the stage of breast cancer at initial diagnosis. However, for tumours measuring 2cm or less, black patients tended to have poorer survival rates than white patients. For tumours larger than 2cm, the survival rate was similar in black and white women.
What interpretations did the researchers draw from these results?
The researchers conclude that tumours in younger black women were more aggressive. Black women were also more likely have basal-like tumours, which are more difficult to treat. Among women with smaller tumours, black women were more than twice as likely to die of their disease. The researchers state that there were no differences between the women in the treatment they received or in their socioeconomic status.
What does the NHS Knowledge Service make of this study?
This is a cross-sectional survey relying on a review of clinical notes from 1994 to 2005. The routine collection of cancer data was standardised in 2001 but before this, researchers had to rely on a search through the computerised discharge summaries for a confirmation of the diagnosis and ethnicity.
When reviewing this study several features are important:
- Fifty-three records were excluded from the analysis because of undisclosed ethnicity. This is more than half the total number of black people analysed and it is unclear how inclusion of this data may have affected the results.
- The researchers compared the age distribution of their sample with that of the population from the census for Hackney. However, it is not clear how any age adjustments were made. It is unusual in this type of study not to standardise the rate of breast cancer using small age bands, as this ensures that any increase or decrease in the numbers of women diagnosed with new breast cancers could not be explained by differences in the age structure of the population. Exactly how the researchers adjusted for age is not reported.
- Although it is possible to assume, as the researchers do, that black women and white women from the same geographical areas to some extent share the same socioeconomic characteristics, it is also important to adjust for this as well. As data was not available on all patients, this adjustment could not have been made for everyone.
- Women in this study had all visited a hospital, and it is not clear how many were detected by screening. Differences in uptake of screening could affect the proportions of women with small tumours.
This study provides an alert to important differences that may exist between two ethnicities found in east London. Although the researchers found a significant difference in the age distributions of cancer in this population and attribute this to ethnic differences, this may not apply to the wider population and there may be other social factors affecting the results. These data should provide an impetus for further studies in this important area.
Sir Muir Gray adds...
This is an important issue as it could allow different screening policies for different ethnic groups.